1. Field of the Invention
The present invention relates to a lens-holding frame for holding a lens group that comprises at least one lens element at a predetermined position.
2. Description of the Related Art
For general configuration of a widely known lens-holding frame, a lens holding barrel having an inside diameter substantially equal to the diameter of a lens held in the barrel, is used as the lens-holding frame body. On the inner surface of the lens holding barrel and on a side close to one end thereof, a ring-shaped rim is formed that extends inwardly to the radial direction from the inner surface along its circumference. A ring-shaped plane of the ring-shaped rim functions as a lens-abutting end-face. Namely, when a lens is inserted inside the lens holding barrel from the opening at the other end of the lens holding barrel, the circumference of the lens abuts against the lens-abutting end-face of the ring-shaped rim. Due to this, the position of the lens inside the lens holding barrel is defined.
On the other hand, a female thread is formed or cut on the inner surface of the lens holding barrel into which a lens-retaining ring is screwed. Thereby, the lens group is held at a predetermined position inside the lens holding barrel by screwing the lens-retaining ring into the lens holding barrel under condition that the leading lens of the lens group inserted inside the lens holding barrel abuts against the lens-abutting end-face.
An object of the present invention is to provide a lens-holding frame comprised of a single piece that can be produced at a relatively low cost and has an advantage in lens mounting efficiency.
According to the present invention, a lens-holding frame for holding a lens at a predetermined position is provided that comprises a frame body, at least two lens-holding arms, and a positioning member.
Each of the lens-holding arms is elastically deformable and supported in a cantilever manner by the frame body, so that the lens-holding arms circumscribe the lens. The positioning member is provided along the inside circumference of the frame body so that the positioning member abuts against a circumferential edge of the lens and defines the holding position of the lens. Each of the lens-holding arms comprises a projection which projects out and penetrates to the inside of the frame body, and a space between the positioning member and the projection is given dimensions and a shape that can receive the circumferential edge of the lens. Further the projection is formed with a tapered surface, so that the circumferential edge of the lens can ride over the projection as a result of the lens-holding arms being elastically pushed open when the circumferential edge of the lens is engaged with the tapered surface and the lens is pushed in toward the positioning member.
The frame body may comprise a connection part which is used for connecting the frame body to a lens barrel, so that the lens-holding frame can be applied to various type of optical systems. When the lens-holding frame is applied to a specific optical system, the frame body may be integrally formed as part of a lens barrel.
To facilitate the processing or optical accuracy of the lens, the lens preferably describes a circular profile. At this time, the lens-holding arms are made to circumscribe a circle having substantially the same diameter as the lens, so that the projections of the lens-holding arms are made to penetrate inside the circle.
Preferably, each of said lens-holding arms comprises a first arm section that extends in parallel with a center axis of the frame body and a second arm section that integrally extends from the first arm section along an arc of said circle. Further, the projection is integrally formed at the front end of the second arm section. Thereby, the total length along the first and second arm sections becomes relatively long even when the first and second arm sections are arranged in a narrow region, so that each lens-holding arm can bear suitable elasticity.
For molding the sleeve-shaped member integrally, the frame body may be configured as a sleeve-shaped member that comprises a synthetic resin material. Further, the inside diameter of the sleeve-shaped member is substantially equal to the diameter of the lens, and the lens-holding arms are integrally formed in the circumferential wall of the sleeve-shaped member. At this time, the positioning member may comprise a ring-shaped abutting end-face that is formed at a ring-shaped rim which integrally extends out from the inner surface of the sleeve-shaped member along the circumference of the inner surface. In another aspect, the positioning member may comprise arc-shaped abutting end-faces that are formed at each of arc-shaped rims. The arc-shaped abutting end-faces integrally extend out from the inner surface of the sleeve-shaped member along the circumference of the inner surface at equal intervals. These constructions may simplify the structure of the positioning member.
From another aspect of the invention, the frame body may be configured as a ring-shaped disk member. The disk member may be comprised of a synthetic resin material. Further, an outside diameter of the ring-shaped disk member is larger than the diameter of the lens, and the lens-holding arms integrally extend out from one side of the ring-shaped disk member in parallel with the center axis of the ring-shaped disk member. This enables further miniaturelization of the lens-holding frame. In this construction, the positioning member may comprise a ring-shaped abutting end-face that is formed on the one side of the ring-shaped disk member along the circumference of the ring-shaped disk member. Further, the positioning member comprises at least two arc-shaped abutting end-faces that are formed at equal intervals on the above one side of the ring-shaped disk member along the circumference of the ring-shaped disk member.